(CBS News) Food allergies are more common in kids who live in a city than those who live in more rural areas, according to new research.
The new study is the first to map children's food allergies by where they live in the United States, according to the researchers. They surveyed parents of nearly 38,500 kids younger than 18, asking for their zip codes and details on their child's food allergy.
The researchers determined that in urban centers, almost 9.8 percent of children had food allergies, compared with 6.2 percent of children in rural communities. Specifically, city children were twice as likely to have peanut (2.8 percent compared to 1.3 percent) and shellfish allergies (2.4 percent compared to 0.8 percent) compared to their rural counterparts. Based on the survey, the states with the highest prevalence of food-allergic kids were Nevada, Florida, Georgia, Alaska, New Jersey, Delaware, Maryland, and the District of Columbia.
"We have found for the first time that higher population density corresponds with a greater likelihood of food allergies in children," study author Dr. Ruchi Gupta, an assistant professor of pediatrics at Northwestern University Feinberg School of Medicine, said in a news release. "This shows that environment has an impact on developing food allergies. Similar trends have been seen for related conditions like asthma. The big question is - what in the environment is triggering them?" A better understanding of environmental factors will help us with prevention efforts."
The study is available online now, and will be published in the July issue of Clinical Pediatrics.
Regardless of location, food allergies were equally severe for the surveyed kids. Nearly 40 percent of food-allergic children surveyed had experienced a severe life-threatening reaction at some point.
Nationwide, about 5.9 million children under 18 have a food allergy, or one out of every 13 kids, Gupta said.
The first time a person with food allergy is exposed to the food, there are no symptoms. But the body has been now been primed, so when the person eats the food again, an allergic response will occur.
An allergic reaction usually takes place within a few minutes to several hours after exposure to the food allergen. The process of eating and digesting food and the location of immune cells involved in the allergic reaction process both affect the timing and location of the reaction, according to the National Institute of Allergy and Infectious Diseases. Symptoms include itching or swelling in your mouth, GI symptoms such as vomiting, diarrhea or abdominal pain, hives or eczema, trouble breathing and a drop in blood pressure.
People may also experience a severe reaction called anaphylaxis within seconds or hours of exposure that affects many different areas of the body. Anaphylaxis can be life-threatening and requires immediate medical attention.